Bore location system

ABSTRACT

A system for locating a horizontal bore below a ground surface includes a transmitting source that radiates from the bore a dipole magnetic field aligned with the bore. A receiver includes a first and a second coil, the axis of each coil being orthogonal to the axis of the other. A measurement device in communication with the coils is configured to measure the phase of signals induced in the coils by the magnetic field when the axis of the first coil is horizontally perpendicular to the axis of the magnetic field and the axis of the second coil is vertically perpendicular to the axis of the magnetic field. The measurement device determines the lateral position of the transmitting source relative to the coils responsively to the phase of the signals induced on the two coils.

BACKGROUND OF THE INVENTION

[0001] This application is a divisional application of copending U.S.patent application Ser. No. 09/657,678 filed Sep. 8, 2000, thedisclosure of which is incorporated herein by reference.

[0002] The present invention relates generally to underground borelocation systems.

[0003] Those of ordinary skill in the art should recognize that the term“horizontal bore” refers to the excavation of a hole, typically forutilities, through the ground and to the excavated hole itself. Thepresent invention relates to systems and methods for locating suchbores, but also to such systems and methods for locating existing buriedutilities, whether such existing utilities were initially installed byboring or trenching techniques. Accordingly, unless otherwise indicated,the term “bore” as used herein refers to new bores and to existingburied utilities or similar lines.

[0004] Boring location systems are utilized in a variety ofcircumstances. For example, in horizontal boring systems as aretypically used for installing utilities, it is desirable to maintain adirectional boring head in a desired boring path and to avoid knownobstacles such as existing utilities. Accordingly, systems are known totrace existing utilities from an above-ground position.

[0005] The boring head, which may include a boring probe behind a drillhead, is underground and is therefore not visible to the operator.Accordingly, the boring probe may be configured to transmit signals fromthe bore that provide location information to an above-ground operator.One system that is configured to determine whether an underground boringprobe is laterally offset from its intended horizontal path is describedin U.S. Pat. No. 4,881,083, the entire disclosure of which isincorporated herein by reference. This information is used, in turn, tomaintain the boring head in its desired path. Typically, however, anabove-ground receiver must be disposed at a known location relative tothe boring head with respect to the head's desired path of travel inorder to properly read certain location information. For example, assumethat a boring head is to the right of its desired path and that anabove-ground receiver is disposed along the path in an attempt toreceive location information from which to determine whether the boringhead should turn to the right or to the left to regain or maintain itspath. Using one conventional receiver, the operator must know whetherthe boring head is ahead of or behind the above-ground receiver withrespect to the desired path.

SUMMARY OF THE INVENTION

[0006] The present invention recognizes and addresses disadvantages ofprior art constructions and methods. Accordingly, it is an object of thepresent invention to provide an improved bore location system.

[0007] This and other objects are achieved by a system for locating ahorizontal bore below a ground surface. The system includes atransmitting source configured to radiate from the bore a dipolemagnetic field aligned with the bore. A receiver includes a first coiland a second coil, the axis of each coil being orthogonal to the axis ofeach other coil. A measurement device in communication with the coils isconfigured to measure the phase of signals induced in the coils by themagnetic field when the axis of the first coil is horizontallyperpendicular to the axis of the magnetic field and the axis of thesecond coil is vertically perpendicular to the axis of the magneticfield and to determine the lateral position of the transmitting sourcerelative to the coils responsively to the phase of the signals inducedon the two coils.

[0008] A method according to the present invention for locating ahorizontal bore below a ground surface includes providing a transmittingsource in the bore and radiating from the bore a dipole magnetic fieldaligned with the bore. A receiver having first and second orthogonallyaligned receiver coils is disposed remotely from the bore so that thedipole magnetic field induces a signal in each coil. A measurementdevice determines the phase of the induced signal of each coil when theaxis of the first coil is horizontally perpendicular to the magneticfield axis and the axis of the second coil is vertically perpendicularto the magnetic field axis. The measurement device determines thelateral position of the transmitting source relative to the coilsresponsively to the phases of the first and second coils.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A full and enabling disclosure of the present invention,including the best mode thereof, directed to one of ordinary skill inthe art, is set forth more particularly in the remainder of thespecification, which makes reference to the appended drawings, in which:

[0010]FIG. 1 is a perspective view of a wireless remote boring system inaccordance with an embodiment of the present invention;

[0011]FIG. 2A is a perspective view of a receiver/transmitter inaccordance with an embodiment of the present invention;

[0012]FIG. 2B is a perspective view of a signal generating probe;

[0013]FIG. 3 is a perspective view of a remote receiver/display inaccordance with an embodiment of the present invention;

[0014]FIG. 4 is a perspective view of a directional boring headassociated with a signal generating probe and drill rod;

[0015]FIG. 5 is a block diagram illustrating the operation of areceiver/transmitter unit in accordance with an embodiment of thepresent invention;

[0016]FIG. 6 is a block diagram illustrating the operation of a remotereceiver unit in accordance with an embodiment of the present invention;

[0017]FIG. 7 is an exemplary visual display of a receiver and/or monitordevice in accordance with an embodiment of the present invention;

[0018]FIG. 8 is an exemplary visual display of a receiver and/or monitordevice in accordance with an embodiment of the present invention;

[0019]FIG. 9 is an exemplary visual display of a receiver and/or monitordevice in accordance with an embodiment of the present invention;

[0020]FIG. 10 is an exemplary bore plot generated in accordance with anembodiment of the present invention;

[0021]FIG. 11A is a perspective view of a transmitting source inaccordance with an embodiment of the present invention;

[0022]FIG. 11B is a perspective view of a transmitting source inaccordance with an embodiment of the present invention;

[0023]FIG. 11C is a perspective view of a transmitting source inaccordance with an embodiment of the present invention;

[0024]FIG. 11D is a perspective view of a transmitting source inaccordance with an embodiment of the present invention;

[0025]FIG. 12 is a schematic illustration of a transmitting source inaccordance with an embodiment of the present invention;

[0026]FIG. 13A is a partial graphical representation of a depthmeasurement procedure practiced in accordance with an embodiment of thepresent invention;

[0027]FIG. 13B is a partial graphical representation of a depthmeasurement procedure practiced in accordance with an embodiment of thepresent invention;

[0028]FIG. 13C is a partial graphical representation of a depthmeasurement procedure practiced in accordance with an embodiment of thepresent invention;

[0029]FIG. 14A is a schematic illustration of control circuitry for usein an embodiment of the present invention;

[0030]FIG. 14B is a schematic illustration of a tilt switch as shown inFIG. 14A;

[0031]FIG. 15 is a schematic illustration of a boring head and tworeceiving coils;

[0032]FIG. 16 is a schematic illustration of a receiver and boring headfor use in a system in accordance with an embodiment of the presentinvention;

[0033]FIG. 17A is a schematic illustration of a receiver and a boringhead for use in a system in accordance with an embodiment of the presentinvention;

[0034]FIG. 17B is a graphical representation of signals induced in areceiver coil for use in an embodiment of the present invention;

[0035]FIG. 17C is a schematic illustration of a receiver and a boringhead for use in a system in accordance with an embodiment of the presentinvention;

[0036]FIG. 17D is a graphical representation of signals induced in areceiver coil for use in an embodiment of the present invention;

[0037]FIG. 17E is a graphical representation of signals induced in areceiver coil for use in an embodiment of the present invention;

[0038]FIG. 17F is a graphical representation of signals induced inreceiver coils for use in an embodiment of the present invention;

[0039]FIG. 17G is a graphical representation of signals induced inreceiver coils for use in an embodiment of the present invention;

[0040]FIG. 18A is a schematic illustration of a receiver and boring headfor use in a system in accordance with an embodiment of the presentinvention;

[0041]FIG. 18B is a schematic illustration of the position of a pair ofreceiver coils and a boring head in determining yaw in accordance withan embodiment of the present invention;

[0042]FIG. 19A is a schematic illustration of a receiver in accordancewith an embodiment of the present invention;

[0043]FIG. 19B is a schematic illustration of a receive in accordancewith an embodiment of the present invention;

[0044]FIG. 19C is a schematic illustration of a multiplexer and CPU foruse in a receiver constructed in accordance with an embodiment of thepresent invention;

[0045]FIG. 19D is a schematic illustration of a multiplexer and CPU foruse in a receiver constructed in accordance with an embodiment of thepresent invention;

[0046]FIG. 20 is a graphical representation of signals induced inreceiver coils for use in an embodiment of the present invention;

[0047]FIG. 21 is a schematic illustration of display icons provided by areceiver constructed in accordance with an embodiment of the presentinvention; and

[0048]FIG. 22 is a schematic top view of a boring machine, a probe in abelow-ground boring tool, and a path taken by an above-ground operatorlocating the probe according to a method in accordance with anembodiment of the present invention.

[0049] Repeat use of reference characters in the present specificationand drawings is intended to represent same or analogous features orelements of the invention.

DETAILED DESCRIPTION

[0050] Reference will now be made in detail to presently preferredembodiments of the invention, one or more examples of which areillustrated in the accompanying drawings. Each example is provided byway of explanation of the invention, not limitation of the invention. Infact, it will be apparent to those skilled in the art that modificationsand variations can be made in the present invention without departingfrom the scope or spirit thereof. For instance, features illustrated ordescribed as part of one embodiment may be used on another embodiment toyield a still further embodiment. Thus, it is intended that the presentinvention covers such modifications and variations as come within thescope of the appended claims and their equivalents.

[0051]FIG. 1 illustrates a directional boring device 10 in accordancewith an embodiment of the present invention. A boring machine 12 islocated in an initial position and includes a boring rod 14 and adirectional boring head 16. The boring machine includes a control panel18 with actuators 20 for controlling operation of the boring device. Ameans for wireless receipt of location signals from a transmittingsource includes a receiver 22. Receiver 22 includes a display 24 and themeans for wireless transmission from the receiver device of informationreceived from the transmitting source to a remote monitor device. Asembodied herein, the means for wireless transmission includes a wirelesstransmitter 26 with an antenna 28.

[0052] A signal generating probe 30 is located generally adjacent boringhead 16 for emitting location signals containing information about theboring device as will be discussed in more detail below. The guidancesystem further includes a remote monitoring device 32 located generallyadjacent to boring machine 12 for receiving the transmitted informationfrom transmitter 26 via wireless transmission. Remote monitor 32includes a display 34 so that the operator 36 of the boring device cansee and/or hear the information transmitted from transmitter 26.

[0053] Accordingly, a workman 38 at a distant location from the boringmachine 12 utilizes receiver 22 to receive a location signal from signalgenerating probe 30, which signal contains information with respect tothe boring head 16. Such information may be, for example, its location,its depth below the ground, its pitch, its angular position or roll, itstemperature, and/or the remaining battery life of the probe. Thisinformation is received by receiver 22 as will be described in moredetail below and is processed on display 24 at this location.

[0054] Substantially simultaneously and in real time, transmitter 26transmits signals carrying the information that is displayed on display24 to the monitor 32 via wireless transmission. Remote monitor 32processes these signals and displays them on display 34. Both data andimage signals may be transmitted between the wireless transmitter andremote monitor 32. Thus, operator 36 at the boring device is able toobtain real time information with respect to the boring head just asworkman 38 is able to obtain this information at the location of theboring head. The particular mechanisms for accomplishing this withrespect to a preferred embodiment are described in more detail below.

[0055] The system may also be used to locate existing utilities. Forexample, referring to FIG. 11A, transmitting source 50 radiates alocation signal from utility 52 located within the bore. Cables fromtransmitting source 50 are clipped directly to buried utility 52 and toground at 54. AC current carries along the length of the conductor andreturns through a grounded stake to transmitter 50, providing a signalloop. Current strength displayed on both transmitter 50 and receiver 22is at its maximum as receiver 22 moves directly over and traces theutility. Receiver 22 may indicate the maximum current by audible orvisual means, thereby indicating the lateral position of the horizontalbore with respect to the receiver device. Thus, an operator carrying aportable receiver device can move to his left or right until thereceiver device is approximately directly above the utility.

[0056] Faults can be detected by current fluctuation. A microprocessorwithin receiver 22 rejects the depth reading when receiver 22 straysover other utilities in the area by indicating “DETECTING ERROR” on thevisual display. Current strength is adjustable to avoid bleeding ontoother utilities in congested areas, and to “power—up” for a longerlocate in areas where no other utilities are present. One transmittingsource configured to operate as described above and below is theSpotDTek® marketed by McLaughlin Manufacturing Company, Inc. ofGreenville, S.C.

[0057] Transmitter 50 may also be configured to indirectly generate thelocation signal when a direct connection to the utility is impractical.For example, referring to Figure 11B, transmitter 50 is placed on theground surface in an upright position above the utility 52. Transmitter50 emits a varying magnetic field 54 to generate a current along utility52 which, in turn, induces a magnetic field along the length of utility52. Accordingly, receiver 22 may detect the location signal. Using theMcLaughlin SpotDTek®, this indirect mode is effective for utilitiesburied at depths of 6.5 feet or less and produces a location signaldetectable up to 200 feet. As in the direct connection mode, “DETECTINGERROR” will be displayed if receiver 22 picks up other utilities in thearea. The current induction strength is adjustable in this mode to tuneout other utilities in congested areas. Current readout on the digitaldisplay also detects faults as receiver 22 is moved along the surface.

[0058] Referring now to FIG. 11C, for depths between 6.5 and 16 feettransmitter 50 is placed over utility 52. A strong signal 54 isgenerated by twin coils, and high AC power provides an effectivedetection range of over 1,000 feet. As in the short span indirect mode,current strength can be fine-tuned so that other utilities and faultsmay be readily deteced.

[0059] Referring to FIG. 11D, a coil clamp can be used on metallic linesor to induce a signal through PVC lines. The coil clamp does not have toclose around the conductor. It need only be placed on and parallel tothe utility 52. The SpotDTek® external coil mode has a detection rangeof over 1,000 feet.

[0060] The above-described methods for detecting an existing utilityinvolve radiating a location signal from a metallic utility. Referringto FIG. 12, a transmitting source for use with nonmetallic pipe includesa battery operated transmitter probe 56 inserted in PVC or othernonmetallic pipe having a 1″ or larger internal diameter. Probe 56 emitsa magnetic location signal 54 that is received by a receiver 22 whichtraces the progress of probe 56 as it is routed through the utility 52.

[0061] Furthermore, the transmitting source may be simply the utilityitself. For example, power and telecommunication lines emit their ownelectromagnetic radiation, which may be used as location signals. Thus,receiver 22 may trace these utilities while detecting the self-emittedlocation signal. The SpotDTek® device may be programmed, for example,for three passive frequencies, 50-60 Hz for live power and 13-17 KHz and18-22 KHz for two radio frequencies. Thus, such utilities may be locatedwithout the need of signal inducement as long as current is flowing onthe lines.

[0062] It should also be understood that the receiver 22 may bestationary. For example, the present invention could be utilized in borehoming systems like those disclosed in Chau et al., U.S. Pat. No.4,881,083 and Bridges et al., U.S. Pat. No. 4,646,277. Furthermore, aswill be apparent to those of ordinary skill in the art, a variety ofsuitable apparatus and methods may be employed to radiate a locationsignal from a bore, to receive the location signal and to determine thedepth of the bore responsively to the received location signal.

[0063] Thus, for example, the receiver may be a fixed device or aportable device carried by an operator to trace a new or existing bore.Similarly, the depth measurement device may measure bore depth in avariety of ways. For example, depth may be measured by determination ofa field gradient of a received location signal, as a function of thepitch angle of a directional boring head or through the proceduresdescribed below. Furthermore, the measurement device may be anindependent device or a device embodied by other system components, forexample the receiver.

[0064] Accordingly, all suitable apparatus and methods for accomplishingthe present invention should be understood to be in the scope and spiritof the present invention. For ease of explanation, however, theremainder of the specification will address an exemplary preferredembodiment for use with a directional boring system as shown in FIG. 1.It should be understood that such an example is provided by way ofillustration only and not in limitation of the invention.

[0065]FIGS. 2A and 2B illustrate receiver 22 and signal generating probe30. Receiver 22 includes a longitudinally extended plastic casing 22 awhich houses the receiving mechanism. Integrated with housing 22 a is adisplay 24 and a handle 22 b for positioning the receiver. Attached tothe receiver is a wireless transmitter 26 whose operation will bedescribed in more detail with respect to FIG. 5. Of course, transmitter26 may be incorporated within the receiver unit. Housing 22 a includes aplurality of horizontally spaced apart coils 23 a, 23 b, 23 c and 23 d(shown in Phantom in FIG. 2a) for receiving signals from the signalgenerating probe 30.

[0066] Signal generating probe 30 generates a magnetic field thatcontains information with respect to the probe that is indicative of theboring head 16. Prior to operation, the system is calibrated to thisfield to permit subsequent depth measurements. At calibration, anoperator activates a calibration mode of operation at the receiver andplaces probe 30 ten feet from the receiver, laterally aligned with andparallel to coil 23 a. In calibration mode, the receiver only measuresthe strength of the signal on coil 23 a induced by the probe's radiatedmagnetic field. Receiver 22 (FIG. 5) stores this value (hereinafter“V₁”) in an EEPROM or other suitable memory at the receiver.Additionally, or alternatively, the receiver may transmit V₁ to memory amonitor 32.

[0067] To determine the probe's depth during operation, the operatorcarries receiver 22 as shown in FIG. 1 and positions the receiver sothat coil 23 a is parallel to the probe's actual or intended path oftravel. In a depth-reading mode, the receiver measures only the strengthof the signal on coil 23 a induced by the probe's radiated magneticfield and stores this value (hereinafter “V₂”) to memory at the receiverand/or monitor 32. A CPU at the receiver determines the probe's depth bythe following equation:

depth=10 ft (V ₁ /V ₂)⁻³

[0068] This value is displayed at displays 24 and 34.

[0069] It should be understood that depth may be calculated in anysuitable manner. Thus, for example, coils 23 a and 23 d may utilize thefield gradient of the magnetic field from the signal generator togenerate information as to the location and depth of the boring head asdisclosed in U.S. Pat. No. 3,617,865 dated Nov. 2, 1971, the disclosureof which is incorporated herein by reference in its entirety. Forexample, to measure the distance of an existing underground utility inan arrangement as shown in FIGS. 11A-11D or 12, the operator may placethe receiver above the utility so that parallel coils 23 a and 223 d areperpendicular to the underground utility. In a depth-reading mode, thereceiver measures only the strength of the signals on coils 23 a and 23d induced by the magnetic field radiated from the utility. Assuming thatthe magnitude of these signals are V₁ and V₂, respectively, the receiverstores these values in its memory. The distance L between coils 23 a and23 d is known and is also stored in the receiver's memory. The depth Xbetween coil 23 a and the existing utility is:

X=L(V ₂/(V ₁ −V ₂))

[0070] It should also be understood that the control of coils 23 a, 23b, 23 c and 23 d may be effected in any suitable means. For example, aCPU in the receiver may control the selection of coil outputs to anamplification and filter circuit, as shown in FIG. 9 of U.S. Pat. No.5,363,926, the entire disclosure of which is incorporated by referenceherein.

[0071] Furthermore, referring to FIG. 14A, the output signals from coils23 a, 23 b, and 23 c may be directed to a signal conditioning circuit 80(as shown in FIG. 9 of the '926 patent) and the receiver's CPU,indicated at 46, through a multiplexer 84 controlled by CPU 46 so thatthe receiver may operate whether in a vertical or horizontal position.Referring to FIGS. 19A and 19B, coils 23 b and 23 c reverse theirorientation with respect to a horizontal ground surface when receiver 22is moved from a horizontal to a vertical position. The CPU, which readsa tilt switch 86 (FIG. 14A), controls multiplexer 84 to direct the coilsignals to the appropriate outputs depending on the receiver's position.Referring also to FIGS. 19C and 19D, when the tilt switch indicates thatthe receiver is in a horizontal position as shown FIG. 19A, the CPUcontrols the multiplexer to direct the signals on coils 23 a, 23 b, and23 c to outputs V₁, V₂, and V₃, respectively. When the receiver is movedto a vertical position as shown in FIG. 19B, the output signal from tiltswitch 86 changes state, and the CPU therefore switches the multiplexerso that the signals on coils 23 b and 23 c are directed to outputs V₃and V₂, respectively, as shown FIG. 19D. Thus, the receiverautomatically operates the same whether the receiver is laid flat on theground or held in a vertical position by the operator.

[0072] The tilt switch may be of any suitable construction, for examplea mercury switch or a mechanical switch shown in FIG. 14B. The tiltswitch includes a first lead 88 and two second leads 90 a and 90 b andmay be disposed in receiver 22 (FIG. 1) so that when the receiver isplaced horizontally on the ground, a metal ball 92 rolls between lead 86and lead 90 a, completing a circuit that delivers a signal to CPU 46.Responsively to this signal, the CPU connects the coil signals to signalconditioning circuit 80 through mulitplexer 84 as shown in FIG. 19C.When the receiver reaches about 30°-40° from the horizontal position tothe vertical position, however, ball 92 rolls into position betweenleads 88 and 90 b. This causes the CPU to switch the multiplexer so thatthe coil signals are directed to the signal conditioning circuit asshown in FIG. 19D.

[0073] In a preferred embodiment, the frequency of the signal output bythe signal generator is approximately 38 KHz. Any suitable frequency maybe utilized, such as, for example, 1.2 KHz, 9.5 KHz, 114 KHz, etc.

[0074] Probe 30 in a preferred embodiment includes a ferromagnetic corewith copper windings on which an electrical current is placed togenerate a dipole magnetic field that is received by receiver 22. Probe30 may be of varying types depending on the application desired and maybe capable of providing a variety of types of information. Mercuryswitches may be provided in a probe 30 around its inside perimeter so asto indicate the angular position or roll of the boring head. When theboring head is rotated to a particular position, the appropriate mercuryswitches close and, therefore, angular position information isgenerated. As is indicated in FIG. 4, a directional boring head 16 has asloped potion 16 a for controlling the direction of the boring head inconjunction with the propulsion of the boring machine. With informationas to the angular location of the sloped portion 16 a, the boring headcan be oriented to proceed in a desired direction. This is referred toherein as the roll of the directional boring head.

[0075] In addition, probe 30 may contain a cradle-type switch forindicating the pitch above or below a horizontal plane or a planeparallel to the surface of the ground at which the directional boringhead is located. Finally, indicators may be contained in the boring headand probe to indicate the battery life remaining in the probe or signalgenerator as well as the temperature of the boring head. All of thisinformation may be conveyed to the receiver through the magnetic fieldgenerated by the signal generator, as described in U.S. Pat. No.5,363,926 referenced above. In one preferred embodiment, the mercuryswitch and cradle switch are replaced by respective accelerometers. Itshould be understood, however, that the particular mechanism used tomodulate the magnetic field to carry the pitch, roll, temperature andbattery life information is not essential to the present invention andthat any suitable arrangement may be used.

[0076]FIGS. 7, 8 and 9 illustrate possible visual displays of thereceiver 22 and/or monitor 32. The display as in FIG. 7 illustrates thedirection of the tapered surface 16 a and pitch angle of boring head 16.The display in FIG. 8 illustrates the depth of the boring head at aparticular instance.

[0077]FIG. 3 illustrates a more detailed view of remote monitor 32.Remote monitor 32 may be held around the neck of operator 36 by strap 40or mounted to boring machine 12 in any suitable fashion. Monitor 32contains a display 34 for displaying the information received fromwireless transmitter 26. Display 34 is capable of displaying informationidentical to the information displayed on display 24 so that theoperator 36 of the boring machine will have the same information as theoperator 38 located at the boring head. In a preferred embodiment,display 34, as well as display 24, includes a clock face readout (FIG.7) for indicating the angular position or roll of the boring head inquadrants, as well as indicators for the remaining information asdiscussed above. It should be understood that a graphic or visualdisplay is one preferred form of display, but within the meaning of“display” or “indicate” as used herein, a voice or audio synthesizercould be substituted or other appropriate audible tones sufficient toconvey the appropriate information to the operator. In addition, remotereceiver 32 includes a touch pad control panel 42 for selecting thedesired information to be displayed, adjusting the volume of the audiblesignal, or for other purposes as would be apparent to one skilled in theart. Display 24 has similar controls.

[0078] Referring to FIG. 4, directional boring head 16 includes a slopedor bent surface 16 a for assisting in the directional propulsion of theboring head as described above. Boring head 16 is connected throughboring rod 14 to boring machine 12. A component of the boring rod 14contains a compartment into which the signal generating probe 30 may beinserted for generating the appropriate signals to convey theinformation with respect to the boring head as described above. As willbe understood by those of ordinary skill in the art, as the boring head16 advances through the bore, additional boring rods are added byoperator 36. Thus, the progression of the boring head 16, and thereforethe length of the bore, may be determined in terms of the number ofboring rods expended.

[0079] Referring to FIG. 5, a block diagram is illustrated providing theoperational characteristics of receiver 22 and wireless transmitter 26to one skilled in the art. As illustrated, receiver 22 receives a signalgenerated by signal generating probe 30 via magnetic field as describedabove. For receipt of pitch, roll, battery life and temperatureinformation, the receiver relies on coil 23 a, represented at 43 in FIG.5. The signal received by coil 43 is filtered and converted from ananalog signal to a digital signal at 44. The digital signal is thenprocessed in a central processing unit 46 to generate the appropriateaudible signal as illustrated at speaker 47 and the appropriate visualsignal through display 24. The conversion of the received signals fromthe probe to a visual display and audible output as illustrated in FIG.5 is done in a conventional manner as would be apparent to one skilledin the art and illustrated, for example, at FIG. 9 in U.S. Pat. No.5,363,926 referenced above. One example of a known commercial productsuitable for this function is the Micro Computerized Pipe Locatormarketed by McLaughlin Manufacturing Co., Inc., 2006 Perimeter Road,Greenville, S.C. 29605.

[0080] In accordance with the present invention, central processing unit46 simultaneously and in real time conveys a signal representative ofthe information displayed on display 24 and sent to audible means 47 towireless transmitter 26. Wireless transmitter 26 includes a frequencyshift keyed modem 48 for receiving the signal from a central processingunit 46 and a transmitter chip 49 for transmitting the signal viawireless means to remote monitor 32. In a preferred embodiment, thedigital signal is transmitted between receiver 22 and transmitter 26 at1200 bits per second. Also, in a preferred embodiment, between modem 48and transmitter 49, the “1” component of the digital signal istransmitted on a frequency of 1500 Hz and the “0” component of thedigital signal is transmitted at approximately 2100 Hz. Of course, theseare by way of example only.

[0081] Wireless transmitter 26 is capable of transmitting data and imagesignals and may be of any conventional type wireless transmitter withsuch capabilities. In a preferred embodiment, wireless transmitter 26has selectable bands and transmits on a frequency of 469.50 MHz or469.550 MHz with an output power of 18 milliwatts. Of course, these areby way of example only. In a preferred embodiment, the transmittercircuit corresponds to the Federal Communications Commission Standardno. ID-APVO29O. The wireless transmitter is capable of transmitting bothdata and image signals and transmits the signals to the remote monitor32 substantially simultaneously with the display on display 24, therebyproviding real time information to the operator 36 of the boring machine12.

[0082] Referring to FIG. 6, the signal transmitted by wirelesstransmitter 26 is received by remote monitor 32 at receiver unit 50.Receiver unit 50 receives on the same frequency at which transmitter 49transmits. In a preferred embodiment, such frequency is 469.50 MHz or469.550 MHz. The circuitry utilized in remote monitor 32 alsocorresponds to FCC Standard ID-APVO29O. The signal received at 50 istransmitted via frequency shift keyed modem 52 to central processingunit 53. In a preferred embodiment, this is an eight-bit signal andrepresents the display and audio components of the signal transmitted tomonitor 32. A band pass filter 54 and carrier detector 56 may beutilized to filter and enhance the signal provided to the centralprocessing unit 53. The filter 54 may filter signals, for exampleoutside of a range of 1100 to 2300 Hz. In this embodiment, carrierdetector 56 provides a one—bit signal to central processing unit 53 asto whether a radio wave is sending or not, and this controls the receiptby the central processing unit 53. The signal between receiver unit 50and band pass filter 54 is conveyed as described above with respect tothe signal between modem 48 and transmitter 49 with respect to thefrequencies. The central processing unit 53 processes the signal toproduce an image on display 34 as well as an audible component, ifdesired via, speaker 58. It should be appreciated that both transmitter26 and monitor 32 may be of conventional design for the wirelesstransmission of data and the image signals, the particulars of which arenot essential to the present invention.

[0083] As discussed above, receiver 22 is also a measurement devicecapable of measuring the depth of the probe below the ground surface.This information is transmitted to, and received by, monitor 32 asdiscussed above. Thus, referring to FIG. 9, display 34 indicates thedepth of the boring head 16 at a particular selected location. In thisembodiment, a depth of four feet five inches is indicated at a distanceof one rod length, where one rod is equal to ten feet. Operator 36 mayrecord this information by depressing an appropriate key on keyboard 60,causing CPU 53 to store the depth data associated with the appropriaterod length in EEPROM 61. As each additional rod is expended, operator 36may cause CPU 53 to record the depth data received by receiver 22. CPU53 has been preprogrammed by operator 36 via keyboard 60 prior to theboring operation to receive depth data in intervals of expended rodswhere each rod length is equal to ten feet. Accordingly, when operator36 depresses a “SET” key on keyboard 60, the current depth measurementat CPU 53 is automatically stored in EEPROM 61 and associated with thecurrent cumulative rod number.

[0084] Thus, as rods are expended and depth data is recorded, depth dataassociated with selected locations along the bore is compiled.Accordingly, a bore map may be generated at display 34 or, for example,at a personal computer included with monitor 32, as illustrated in FIG.10. The vertical axis of the plot of FIG. 10 indicates feet below groundsurface. The horizontal axis provides the length of the bore in thenumber of rods and rod feet. Thus, at the first extended rod, the boreillustrated was two feet deep while at the tenth rod the bore was nearlyeight feet. Of course, the cumulative data may be presented in a varietyof fashions, for example in tabular form. Accordingly, any and allsuitable methods of identifying the compiled data should be understoodto be within the scope of the present invention.

[0085] A system including the above described mapping capabilities isthe MOLE MAP™, marketed by McLaughlin Manufacturing Company, Inc., 2006Perimeter Road, Greenville, S.C. 29605. This system includes thecapability to change the units at which depth measurements are taken.For example, in programming CPU 53, keys on keyboard 60 may be used toadjust the length of the rods in a boring system. Thus, by adjusting therod length utilized by CPU 53, an operator may configure the system torecord depth measurements at a partial rod length or at multiple rods.As the predetermined number of rods are expended, the operator wouldthen press the “set” key on keyboard 60 to record the depth data at thatpoint. Of course, those of ordinary skill in the art should understandthat it is possible to create a control system that would automaticallyrecord the depth data received from receiver 22 as the rods areexpended. As noted above, a map may be generated as in FIG. 10 atdisplay 34 or at a PC included with monitor 32 as indicated in FIG. 6.The plot data is provided to the PC via driver 62 and RS-232C connector63 as indicated. Alternatively, monitor 32 may be embodied by a PCdevice. The information may be provided to the PC in real time as thedepth data is recorded by operator 36 via keyboard 60. Furthermore, acumulative plot stored in EEPROM 61 may be downloaded to a PC andprinter via connector 63. It should be understood, however, that monitor32 may or may not include a PC.

[0086] As discussed above, the present system may be used to mapexisting utilities. In such a configuration, CPU 53 may be programmed toreceive depth data in intervals of actual ground distance. Thus, anoperator 38 as in FIG. 1 traces the existing utility with receiver 22.As the operator moves away from a starting point, operator 36 recordsdepth data on a monitor at predetermined intervals from the startingpoint. Thus, a map of an existing utility similar to the map shown inFIG. 10 may be generated. However, the horizontal axis would bestructured in terms of actual distance rather than rod lengths. Monitor32, via CPU 53 or a personal computer, may be configured to mergeexisting utility plots with a boring system plot. Of course, thehorizontal axis of either the boring system plot or the utility plotmust be converted so that the maps are compatible.

[0087] Referring again to FIG. 10, existing utilities runningperpendicular to the new bore are indicated. Such utilities are knownutility positions which the new bore must avoid. Accordingly, theability of operator 36 (FIG. 1) to view a bore plot as the bore is beingmade enables the operator to control the directional boring head bycontrols 20 to avoid such existing utilities.

[0088] As noted above, stationary receiver devices may be used inpreferred embodiments of the present invention to generate a boringsystem plot. One method of measuring bore depth with respect to theground surface in such a system utilizes the pitch angle of thedirectional boring head. Referring to FIG. 13B, a bore is graphicallyillustrated beginning at ground level at 70. The first ten foot rodsection is expended at a 45° angle, and, thus, the depth of the bore atthe first rod is 7.1 feet as shown. The pitch angle at the directionalboring head may change as new rods are expended. In FIG. 13B, the pitchangles at the second, third, fourth, and fifth rods were 30°, 10°, 0°,and 0°, respectively. The depths at these points are 12.1 feet,

[0089] feet, 13.8 feet, and 13.8 feet, respectively.

[0090] This depth information may be transmitted from a stationaryreceiver device to a monitor device for use in generating a bore plot asdescribed above. Again, the horizontal axis may be presented either interms of expended rods (FIG. 10) or in actual ground distance. Forexample, if a plot were generated from the depth information of FIG.13B, a depth of 7.1 feet would be marked at 1 rod (or 10 feet if a rodis 10 feet long) while a depth of 12.1 would be marked at 2 rods. If theplot is presented in terms of ground distance, a depth of 7.1 feet wouldbe marked at 7.1 feet from starting point 70 while a depth of 12.1 feetwould be marked at 15.76 feet from point 70.

[0091] An accurate plot may be generated from the information as in FIG.13B if the ground surface is substantially level. If the bore is madebelow a ground surface that is not level, the depth information of FIG.13B must be modified if an accurate plot is to be obtained. For example,FIG. 13A graphically represents exemplary depth measurements made ateach of the rod positions along the bore represented in FIG. 13B by, forexample, a portable measurement device as described above. The depthdata from FIG. 13B may then be modified to determine the position of thebore 52 with respect to an actual ground surface line 72 as illustratedin FIG. 13C. The adjustment may be made by a central processing unitsuch as CPU 53 as in FIG. 6.

[0092] It should also be understood by those of ordinary skill in theart that receiver 22 may also be configured to compile the dataassociated with the selected locations as described above with respectto monitor 32. That is, monitor 32 may be at least partially embodied bya receiver 22. This may be particularly advantageous in systems whereonly a utility plot is desired. In such case, a transmitting sourceradiates the location signal from the bore as described above, while asingle portable unit may be used to receive the location signal, measurethe depth, and compile the depth data associated with the selectedlocation. Thus, a single apparatus would encompass the receiver device,measurement device and monitor device. Of course, in a directionalboring system as shown in FIG. 1, receiver device 22 may be configuredto simultaneously provide the same display as presented to the operator36 at monitor 32.

[0093] The receiver may also be used to measure a diagonal distancebetween probe 30 and receiver 22. Referring to FIG. 15, the measurementis based on the relationship between the probe and two coils. Forexample, if a probe 30 radiates a dipole magnetic field, indicated at96, and coils a and b are disposed at equal distances from probe 30 asshown in the figure, the magnitude of the induced signal across coil ais twice the magnitude of the signal induced across coil b. Referringnow to FIG. 16, receiver 22 is placed on the ground so that coil 23 b isaligned with the probe 30. Where V₁ is the calibration voltage discussedabove, V₂ is the magnitude of the induced signal on coil 23 b, and V₃ isthe magnitude of the signal induced across coil 23 c,

V ₄=((V ₃)²/(V ₂)²)^(0.5.)

[0094] The distance X between probe 30 and receiver 22 is:

X=10 ft(V ₁/2V ₄)⁻³

[0095] The diagonal measurement X may be used to locate probe 30 whenthe probe is below a surface, such as a busy road or a body of water, inwhich the operator is unable to carry receiver 22. As discussed above,the probe's position, including the depth Y below the ground surface,may be determined through measurements of the probe's pitch angle ateach rod section. Assuming that the ground surface is approximatelylevel between receiver 22 and probe 30, the horizontal distance Zbetween the probe and the receiver is (X²-Y²)^(0.5). The receiver's CPUmay perform this calculation and present the result at the receiver'sdisplay. Accordingly, an operator may place the receiver at the edge ofthe road or body of water and determine how far the probe has yet totravel to reach the edge.

[0096] Referring to FIGS. 18A and 18B, receiver 22 may be used todetermine the yaw of probe 30 with respect to its intended path oftravel 98. The operator holds receiver 22 in a vertical position aboveprobe 30 so that coil 23 a is aligned with path of travel 98. As shownin FIG. 18B, coil 23 c is therefore perpendicular to path 98. The angleΘ is equal to arctan(V₁/V₂), where V₁ is the magnitude of the signalinduced in coil 23 c, and V₂ is the magnitude of the signal induced incoil 23 a.

[0097] Referring again to FIG. 18A, the yaw calculation loses accuracy,but may still be effective, where receiver 22 is moved forward or backalong path 98 or directly laterally from path 98. The acceptabledistance from the probe depends on the probe's depth and the amount ofaccuracy reduction the operator is willing to accept. An operator mayuse this feature in guiding the boring tool. For example, an operatormoving forward along path 98 ahead of probe 30 may monitor the yaw ofthe probe as it follows underground. Assuming the yaw reading is zerodegrees as the operator moves away from the probe, the yaw will remainzero degrees during drilling if the probe remains on course. A change inthe yaw instantly tells the operator the appropriate angle by which thedrilling tool is moving off course, and the drilling head may then beturned back toward its intended course.

[0098] The receiver may also be used to determine the probe's lateraldeviation from its intended path using two perpendicular coils, one ofwhich is aligned with the probe's intended path and one of which ishorizontally aligned perpendicular to the path. This method is effectivewhere the receiver is sufficiently in front of the probe. Where theprobe is close to or in front of the receiver, the method is effectiveif the operator knows the relative positions of the probe and receiveralong the probe's desired path. Referring to a side view of receiver 22on a ground surface 104 presented in FIG. 17A, a locating coil (23 a) isaligned with horizontally perpendicularly to the probe's path of travel.Coil 23 b, which is aligned with the probe's path, is the referencecoil. Referring also to FIG. 17B, magnetic field 96 induces a signal 106in coil 23 b. When coil 23 b is in front of a line 108 at which the fluxlines of field 96 pass perpendicularly through the coil, signal 106 hasa phase as referenced to the left of line 108 in FIG. 17B. As probe 30moves beyond this point, so that coil 23 b is between line 108 and aline 110 at which the magnetic flux lines behind the probe passperpendicularly though the coil, signal 106 changes phase by 180degrees. As the probe continues, so that coil 23 b moves behind line110, signal 106 returns to its original phase.

[0099]FIG. 17C is a top view of probe 30 with respect to receiver 22,which is aligned parallel to the probe's intended path of travel 98.Probe 30 induces a signal in coil 23 a if probe 30 is to the left orright of path 98. The phase of the induced signal, however, depends uponwhether the probe is before or beyond, with respect to path 98, a line112 aligned with coil 23 a. Referring also to the left hand side of FIG.17D, if probe 30 is before line 112, an induced signal 114 in coil 23 acan have either of two opposite phases depending on whether it is to theleft or right of path 98. When the probe passes beyond line 112, signal114 changes phase by 180 degrees. That is, the phase of signal 114changes across both lines 98 and 112.

[0100] Referring now to FIGS. 17A-17D, the probe's lateral position withrespect of its intended path of travel 98 is described by a comparisonof signals 106 and 114. This comparison depends, however, on therelative position of the probe and the receiver. If probe 30 andreceiver 22 are disposed so that coil 23 b is in front of line 108 (theprobe is therefore also before line 112), a relationship between thesignal on coil 23 a and the signal on coil 23 b describes the probe'slateral position. If signal 106 is in phase with signal 114, the probeis to the left of line 98. If the signals are out of phase, the probe isto the right of line 98. That is, the probe is to the left of itsintended path if the signal in the locating coil is in phase with thereference signal and is to the right of path 98 if the signals are outof phase. This relationship between the locating and reference signalsis hereinafter referred to as the “direct” relationship, although itshould be understood that use of the terms “direct” and “inverse” todescribe phase relationships herein is for purposes of explanation only.It should also be understood that the relative phase between any twocoils also depends upon the orientation of the signal measurement acrossthe coils. Of course, such physical arrangements will be known for agiven receiver, and the receiver's CPU may be programmed accordingly.

[0101] The opposite relationship, hereinafter referred to as the“inverse” relationship, is demonstrated between lines 108 and 112. Here,signals 106 and 114 are out of phase when the probe is to the left ofline 98 but are in phase when the probe is to the right. Between lines112 and 110 signals, 106 and 114 return to the direct relationship. Ascoil 23 b moves beyond line 110, the signals revert to the inverserelationship.

[0102] As indicated in FIGS. 17A-17D, the operator and/or the receiver'sCPU must know the relative position of the receiver and the probe withrespect to path 98 where the determination of the probe's lateralposition with respect to line 98 is based only on the phase relationshipbetween the signals induced on coils 23 a and 23 b. Where the receiveris sufficiently in front of the probe, so that coil 23 b is in front ofline 108, the CPU may rely on the direct relationship, and this can bethe default relationship to which the CPU is programmed. A button may beprovided at the receiver by which the operator may change the CPU tobase its determination on the inverse relationship. To effectively usethis feature, however, the operator must know the relative position ofthe receiver and the probe to switch between the modes at the crossingsof lines 108, 112 and 110.

[0103] Referring again to FIG. 17A, and also to FIG. 17E, the inclusionof coil 23 c eliminates the need for the operator or the CPU to know therelative position of the probe and the receiver with respect to theintended path. As probe 30 moves up to and past a line 118 aligned withcoil 23 c, magnetic field 96 induces in the coil a signal 120 thatchanges phase by 180 degrees as the probe passes line 118. Referringalso to FIG. 17C, lines 112 and 118 are separated by the distanceseparating coils 23 a and 23 c. This distance is, however, relativelysmall, and for the purposes described herein the lines may be consideredaligned with each other. Under this treatment, comparison of FIGS. 17Dand 17E shows that the direct relationship applies between signals 120and 114 regardless of the relative position of probe 30 and receiver 22with respect to path 98. Thus, where coil 23 c is the reference coil,the receiver's CPU may determine whether the probe is to the left or tothe right of path 98 using the direct relationship at all times.Accordingly, in one embodiment of the present invention, the receiver'sCPU may be programmed to employ this relationship.

[0104] Because signals 114 and 120 both go to zero when the probereaches the receiver, the receiver in one preferred embodiment selectseither coil 23 b or 23 c as the reference coil, depending on the coils'relative signal strength. FIGS. 17F and 17G illustrate the magnitudes ofsignals 106, 114 and 120 as the probe and the receiver move in parallelpast each other and across lines 108, 112/118 and 110. The horizontalaxis in each figure describes the relative longitudinal position betweenthe probe and the coils. The vertical axis describes the magnitude ofthe signals induced on the coils. The position of a signal line above orbelow the horizontal line reflects the signal's phase, and this providesthe difference between the figures. In FIG. 17F, the probed is always tothe left of line 98 (FIG. 17C), while in FIG. 17G, the probe is to theright. Since the probe's lateral position with respect to line 98determines the phase of the signal on coil 23 a, the phase of line 114changes by 180° from FIG. 18F to FIG. 17G. These figures againillustrate that, as embodiment described above, the probe's lateralposition relative to line 98 may be determined from a comparison of thephase of signals 114 and 120 alone. The plots in FIGS. 17F and 17G areprovided for purposes of explanation and are not to scale.

[0105] In this embodiment, the receiver's CPU monitors the magnitude(the absolute value) of signals 106 and 120 and chooses the referencecoil depending upon which signal has the greater magnitude. That is, ifthe magnitude of 106 is greater than that of signal 120, coil 23 b isthe reference coil. On the other hand, coil 23 c is the reference coilwhen signal 120 has the greater magnitude. Accordingly, coil 23 b is thereference coil in zones 122, 124 and 126 shown in FIG. 17F and 17G, andcoil 23 c is the reference coil in zones 128 and 130.

[0106] As discussed above, however, a comparison of induced signalsalone is insufficient to determine the lateral position of the probewith respect to the receiver when coil 23 b is the reference coil.Accordingly, the receiver's CPU also monitors the relative phase betweensignal 106 induced in coil 23 b and signal 120 induced in coil 23 c. Atthose times when coil 23 b is chosen as the reference coil (i.e. inzones 122, 124 and 126), the use of the direct and inverse relationshipsbetween signal 114 and signal 106 depends on the relative phase betweensignal 106 and signal 120. If signal 106 is in phase with signal 120,the CPU uses the direct relationship between signal 106 and signal 114to determine the probe's lateral position. If signal 106 is 180° out ofphase with signal 120, the CPU uses the inverse relationship betweensignal 106 and signal 114 to determine the probe's lateral position.When the CPU detects that signal 106 and signal 120 are out of phase,the CPU may reverse the polarity of the measurement access coil 23 b anduse the direct relationship between signals 106 and 114.

[0107] Coil 23 c is the reference coil in zones 128 and 130. Asdiscussed above, the CPU always uses the direct relationship betweensignals 120 and 114 in determining the probe's lateral position whencoil 23 c is the reference coil.

[0108] Upon determining the probe's lateral position with respect toline 98 (FIG. 17C), the receiver's display 24, and/or the monitor'sdisplay 34, displays an arrow indicating which direction the probe needsto move in order to regain line 98. That is, when the receiver isaligned with line 98 as shown in FIG. 17C, the display arrow points tothe right when the probe is left of line 98 and points to the left whenthe probe is to the right of the line.

[0109] Referring to FIG. 22, an operator may locate the ground positionof probe 30 using the above-ground receiver 22 (FIG. 1). Starting atdrilling machine 12, the operator activates the receiver's locating modeand begins walking toward the position he believes the probe to be. Thatis, he begins walking along a path 154 he believes to be longitudinallyaligned with the probe. Of course, the operator's path likely divergesfrom the probe's underground longitudinal line (i.e. the axis of themagnetic field radiated by the probe), indicated in FIG. 22 at 156. Bystarting at the drilling machine, however, the operator can make areasonable estimate of the probe's longitudinal line and can carry thereceiver so that the axis of coil 23 c (FIG. 1) is aligned at an oblique(i.e. parallel or less than 90°) angle with respect to the probe'slongitudinal line. Preferably, this oblique angle is within a range from0° to 45°.

[0110] As the operator walks, he views the receiver's display. Referringalso FIGS. 20 and 21, the display provides a sequence of icons as shownin FIG. 21, which are in turn based on signals 106 and 120 induced incoils 23 c and 23 b, respectively, by the probe's magnetic field.Assuming that the receiver is in its vertical position as shown in FIG.19B, FIG. 20 illustrates signals 106 and 120 as the receiver moves upfrom behind the probe along line 154 to a line 156 extending laterallyfrom the probe, and then beyond the lateral line. To the left of thevertical axis in FIG. 20, the receiver is behind lateral line 156. Tothe right of the vertical axis, the receiver is in front of the lateralline.

[0111] A line 132 in FIG. 20 illustrates the square root of the sum ofthe squared values of lines 106 and 120. The receiver's CPU determinesthis value as the operator moves along line 154. Initially, when theoperator activates the receiver's locating mode, the receiver's displayshows an icon 134. As the operator moves, the receiver monitors thevalue represented by line 132. If line 132 decreases, meaning that theoperator is moving away from the probe, icon 134 does not change. Thisinforms the operator that he is moving away from the probe. If theoperator moves toward the probe, line 132 increases, and the receiverchanges icon 134 to icon 136, thereby notifying the operator that he ismoving toward line 156.

[0112] The receiver also monitors a comparison value that is equal tothe strength of signal 120 divided by the strength of signal 106. Ifsignals 106 and 120 are out of phase with each other, this value isnegative. If the signals are in phase, the comparison value is positive.As indicated in FIG. 20, the greatest divergence between signals 106 and120 occurs when the receiver is on line 156, and the magnitude of signal120 only falls below 10% of the magnitude of signal 106 within arelatively small distance on either side of the line, as indicated bylines 138 and 140.

[0113] While moving along line 154 toward line 156 from behind, thecomparison value falls below 10% as the receiver reaches line 138. Atthis point, icon 136 changes to an icon 142 informing the operator thatthe receiver is close to and behind the probe's lateral line.Alternatively, the display may provide a position-neutral icon 144 tosimply inform the operator that the receiver is near the line. As theoperator continues forward, the comparison value drops below 6%. At thispoint, icon 142 changes to an icon 146, indicating that the receiver isdirectly over line 156.

[0114] As the operator continues beyond and in front of the probe, thecomparison value becomes negative. When the comparison value falls below−6%, icon 146 changes to an icon 148 that informs the operator he hasnow moved in front of the lateral line. If the operator continues movingforward, icon 148 changes to icon 134 when the comparison value fallbelow −66%.

[0115] If the operator continues to move forward, as indicated at arrow150 in FIG. 21, line 132 continues to decrease, and the receiver'sdisplay continues to provide icon 134. If the operator carries thereceiver back toward the lateral line, as indicated at arrow 152, line132 increases, and the receiver again provides icon 136 and monitors thecomparison value. When the comparison value rises above −10%, thereceiver displays icon 148 or 144. As the operator moves directly abovethe lateral line, and the comparison value rises above −6%, the receiveragain displays icon 146. As the operator moves behind the probe, and thecomparison value rises above 6%, the receiver displays icon 142, whichreturns to icon 134 when the comparison value rises above 66%.

[0116] Once the operator locates lateral line 156, he can follow theline to the probe. To stay on the line while walking, the operatorwatches the receiver's display and maintains a path so that the displaycontinues to show icon 146. Of course, at the time he locates line 156,the operator doesn't know whether he should move to the left of rightalong the line. This information is provided by an indicator on thereceiver's display that is proportional to the magnitude of the signalinduced on coil 23 c, which is held perpendicular to line 156 andtherefore parallel to the probe. When this indicator reaches a maximum,and the display also shows icon 146, the receiver is directly above theprobe. The operator may then accurately determine the probe's headingusing the yaw measurement described above.

[0117] Using the above-described method, the operator may locate thebore. It should be understood, however, that the comparison value rangesmay vary as desired.

[0118] It should be understood that modifications and variations of thepresent invention may be practiced by those of ordinary skill in the artwithout departing from the spirit and scope of the present invention,which is more particularly set forth in the appended claims.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention so further described in such appended claims, andthat the aspects of varying embodiments may be interchanged in whole orin part.

What is claimed is:
 1. A system for locating a horizontal bore below aground surface, said system comprising: a transmitting source configuredto radiate a magnetic field from said bore; a receiver remote from saidtransmitting source and having a plurality of coils disposed so thateach said coil occupies a predetermined operative position with respectto a horizontal plane when said receiver is disposed in a first positionwith respect to said horizontal plane and so that at least one firstsaid coil moves into said operative position of a second said coil whensaid receiver is rotated to a second position with respect to saidhorizontal plane; a processor; and a control circuit in communicationwith said coils to receive signals on said coils induced by saidmagnetic field and in communication with said processor to output saidsignals to said processor, wherein said control circuit is configured todetect said position of said receiver and to replace said signal of saidsecond coil output by said control circuit to said processor with saidsignal of said first coil when said control circuit detects that saidreceiver is in said second position.
 2. The system as in claim 1,wherein said receiver includes a plurality of said first coils.
 3. Thesystem as in claim 1, wherein said second position of said receiver is90° offset from said first position of said receiver.
 4. The system asin claim 1, wherein said control circuit includes a tilt switch.
 5. Thesystem as in claim 1, wherein said control circuit includes amultiplexer through which said signals are directed between said coilsand said processor.
 6. The system as in claim 5, wherein said controlcircuit includes a tilt switch that outputs a signal to said processorthat changes state between said first position of said receiver and saidsecond position of said receiver, and wherein said processor controlssaid multiplexer responsively to said tilt switch signal so that, whensaid tilt switch signal is in a first said state, said multiplexerdirects said signal of said first coil to a first multiplexer output anddirects said signal of said second coil to a second multiplexer outputand, when said tilt switch signal is in a second said state, moves saidsignal of said first coil to said second multiplexer output.
 7. A systemfor locating a horizontal bore below a ground surface, said systemcomprising: a transmitting source configured to radiate a magnetic fieldfrom said bore; a receiver remote from said transmitting source andhaving a plurality of coils disposed so that each said coil occupies apredetermined operative position with respect to a horizontal plane whensaid receiver is disposed in a first position with respect to saidhorizontal plane and so that at least one first said coil moves intosaid operative position of a second said coil when said receiver isrotated to a second position with respect to said horizontal plane,wherein each said coil defines an axis orthogonal to said axis of eachother said coil; a processor; and a control circuit in communicationwith said coils to receive signals on said coils induced by saidmagnetic field and in communication with said processor to output saidsignals to said processor, wherein said control circuit includes a tiltswitch that outputs a signal to said processor that changes statebetween said first position of said receiver and said second position ofsaid receiver and wherein said control circuit is configured to replacesaid signal of said second coil output by said control circuit to saidprocessor with said signal of said first coil when said control circuitdetects that said receiver is in said second position.
 8. The system asin claim 7, wherein said receiver includes a plurality of said firstcoils.